Objective: To evaluate the effect of a behaviour modification program, taught to parents in a single visit to a trained nurse, in improving sleep performance in newborn infants. Design: Randomised controlled trial. Setting and participants: 268 families with normal newborn infants in the community, recruited between October 1996 and March 1997 from birth notices published in a South Australian daily newspaper. Intervention: A 45-minute consultation with a nurse 2-3 weeks after the birth, including a tutorial discussion on normal sleep patterns in newborn infants, supported by retained written material and, for infants with weight gain < 30 g daily, referral to their usual postnatal care provider. Main outcome measures: Hours of daytime sleep (0600-1800), night sleep (1800-0600) and total sleep per 24 h; and number of daily records with total sleep >= 15 h per 24 h, assessed by 7-day sleep diary at ages 6 and 12 weeks. Results: 268 families returned at least one sleep diary (137/171 intervention, 131/175 control), recording 3273 days. Two intervention infants were referred for low weight(gain. Total sleep time was 15 h or more per 24 h on 62% of recorded days in the intervention group, compared with 36% in the control group (P < 0.001). At 6 weeks of age, intervention infants slept a mean 1.3 h per day more than control infants (95% CI, 0.95-1.65), comprising a mean 0.5 h more night sleep (95% CI, 0.32-0.69) and 0.8 In more daytime sleep (95% CI, 0.56-1.07). At 12 weeks, intervention infants slept a mean 1.2 h per day more (95% CI, 0.94-2.14), comprising 0.64 h more night sleep (95% CI, 0.19-0.89) and 0.58 h more daytime sleep (95% CI, 0.39-1.03). There was no significant difference in crying time between the groups. Conclusions: A single consultation supported by written material in the first 3 weeks of a child's life improves sleep performance at 6 weeks of age. This improvement is maintained at 3 months.